Abstract: Due to the non-Newtonian behavior of heavy oil, the seepage characteristics in porous medium are different from conventional crude oil. They usually seep in nonlinear ways and there might exist threshold pressure gradients. Only when the displacement pressure gradient is greater than the threshold pressure gradient, heavy oil begins to flow, and the seepage rule deviates from Darcy's law. Through laboratory experiments, this paper designs a method for measuring threshold pressure gradient appropriately. Natural core samples and simulated oil are used to measure threshold pressure gradient by setting different flow rates. In this way, the impact of flow rate on threshold pressure gradient is studied. The results show that the threshold pressure gradient would be affected when the displacing rate exceeds a critical value. Therefore, in the process of measuring real threshold pressure gradient of a core, the choice of experimental method and displacing rate can not be ignored.